Project Summary/Abstract The goals of this application are to understand the epigenetic and molecular mechanisms that control orofacial bone aging and osteoporosis in parallel with long bones and explore the extent to which targeting epigenetic factor could prevent orofacial bone aging and promote dental, oral and craniofacial tissue regeneration. Aging causes significant changes to bone, characterized by a decrease in the adult stem cell pool, self-renewal and trabecular bone formation, and an increase in marrow adipose tissue accumulation. Orofacial bone, especially alveolar/trabecular bone, is a dynamic and self-renewing tissue with high turnover rate which often dramatically decreases with aging. Mesenchymal stem/stromal cells (MSCs) are adult stem cells in long and orofacial bones and are responsible for continuous tissue renewal, regeneration, and repair. MSCs derived from orofacial bone tissues (OMSCs) are excellent sources for craniofacial bone regeneration due to their closer embryonic origins to the injured sites. Over the past decade, significant progress has been made in understanding the molecular mechanisms governing skeletal aging and osteoporosis. However, little is known about how epigenetic factors control skeletal homeostasis and aging, specifically orofacial bone aging. Using siRNA screening, we discovered that the histone demethylase KDM4B played a critical role in osteogenic differentiation of BMSCs by erasing trimethylated histone H3 at lysine 9 (H3K9me3). The expression of Kdm4b was significantly downregulated in BMSCs isolated from aging mice compared to young mice. To explore the functional role of KDM4B in orofacial bone homeostasis and aging, we utilized Prx1Cre mice to delete Kdm4b in limb and cranial mesenchyme. We found that the deletion of KDM4B accelerated orofacial bone aging and osteoporosis by reducing bone formation and increasing adipogenesis. Importantly, we also identified that parathyroid hormone (PTH), which has been showed to regulate MSC stemness and fate decision, induced Kdm4b in OMSCs. Based on these exciting studies, we hypothesize that KDM4B is a critical epigenetic factor which controls orofacial bone aging and OMSC stemness, and induction of KDM4B promotes OMSC-mediated craniofacial bone regeneration. To test our hypothesis, we propose the following three specific aims: 1) To determine whether KDM4B plays a critical role in regulation of fate decision, osteogenesis and self-renewal of OMSCs in parallel with BMSCs; 2) To determine whether induction of KDM4B prevents orofacial bone aging and promotes orofacial bone regeneration in vivo in parallel with long bones; and 3) To explore epigenetic mechanisms by which KDM4B controls orofacial bone aging and self-renewal of OMSCs in parallel with BMSCs. New findings from our studies will have important implications in developing innovative therapeutic strategies for preventing orofacial bone aging and promoting craniofacial bone regeneration.